High frequency oscillator



pri 2, 1936. C, W. HANSELL.

HIGH FREQUENCY O-SCILLATOR Filed Deo. '7, 1952 INVENTOR- CLARE E W. HANSELL m7 /g/wwt..

ATIIORNEY- Patented Apr. 21, 1936 UNITED STATES PATENT OFFICE HIGH FREQUENCY OSCILLATOR Application December 7, 1932, serial No. 646,040

7 Claims.

This invention relates to the generation of high frequency oscillations and, more particularly, concerns an improved oscillator of the magnetron type.

In the operation of magnetron oscillators, it is customary to control the production of oscillations and the frequency thereof by means of a magnetic field, such as may be caused by a coil surrounding the outer shell of the oscillator. The frequency of oscillations thus produced is dependent upon the time of travel of the electrons in a path from the filament to the anode and back to the filament, the path of electrons being, of course, under the influence of the magnetic field. My conception of the operation of the magnetron oscillator, as set forth in detail in my United States Patent No. 2,001,133, granted May 14, 1935, is that the electronsv in the tube react upon one another in groups so as to produce a whistle effect. In such type of magnetron, it is noted that all of the electrons which strike the anode do so at a time when their velocity is quite high and, consequently, the heating of the anode is considerable and the efliciency is low.

This difculty is overcome in accordance with the present invention by the provision of an oscillator in Which the electrons are absorbed at a time when their kinetic energy is relatively small, thereby causing the generation of oscillations at high eiciency. This method of absorbing electrons reduces energy losses, and is accomplished by placing around the lament of the magnetron a grid or mesh of Wires supplied with a high positive potential. The anode of the tube is given a much higher positive potential corresponding approximately to the potential which would be used in the ordinary magnetron oscillator. 1n the present instance, however, the magnetic iield` is made somewhat higher for a given anode potential than in the usual type of magnetron and results in preventing most of the electrons from ever reaching the anode. Thus the anode is effective in accelerating the electrons away from the vicinity of the filament and the grid, but the magnetic iield makes them follow a curved path back to the grid where all the energy stored in the electrons not moving towards the anode is given up again. After starting to return in their path of travel, a considerable portion of the electrons have a tendency to stop at the grid which is positive with respect to the filament. Upon their arrival in the vicinity of the grid, however, it will be found that their velocity has been reduced to a low value due to the effect of the electrostatic field of the anode which retards the mo- (Cl. Z50-17) tion of the returning electrons. Consequently, the electrons will be absorbed on the grid with` relatively small energy loss. The total input to the tube can thus correspond more nearly to the useful output than would be the case if the electrons were absorbed on the anode at a time when they have high velocity and produce high losses.

Another advantage of the present invention is that the strength of oscillations may readily be controlled by means of the potentials on the electrodes. n

A feature of the invention lies ln the circuit means provided for enabling tuning of the respective grid and anode circuits.

The accompanying drawing illustrates a system embodying the principles of the present invention in which there is shown a magnetron tube comprising a cylindrical anode A, a filament F at the longitudinal axis of said anode, and a grid G surrounding the filament, the whole being sur- 1.

rounded by a field coil C for producing an intense magnetic field in a direction parallel to the axis of the filament. A low positive potential is supplied to the grid G over a lead L, and a much higher positive potential is supplied to the anode through a serially connected telegraph key K. Telegraph key K is merely illustrative of any suitable means for modulating the oscillations and is shown serially connected in the lead M from the source of high positive potential S to the cylindrical anode A. For tuning the electrodes to a desired frequency there are provided by-pass condensers B, B which have movable sliders which are arranged to slide over the connections L and M to the electrodes. Theseare adjusted until the lengths of leads are correct for tuning the electrode capacities in the tube for producing optimum oscillating conditions.

Coupled to the lead L which connects the grid G to the source of potential S is any type of output circuit O which, in turn, may be connected by means of a transmission line TL to-an antenna. Ii desired, tuning elements such as trombone slides T1 and T2 may be inserted in the output circuit for tuning the line to the desired frequency The operation of the tube in producing oscillations is as follows: l v

The positive potential on 'the grid G causes a number of electrons to move from the filament F to the grid, and a large portion of them pass through the grid G and are attracted toward the anode A. Due to the action of the magnetic eld which is substantially parallel to the filament and, hence, substantially at right angles to the electric field acting upon the electrons, the electrons are deflected and caused to travel in a spiral path about the cathode on their way to the anode. The path of these electrons traveling toward the anode is bent and for the proper value of field relative to the anode voltage, the electrons Will describe a loop in passing from the larnent F through the grid G to the vicinity of the anode A and back to the grid G, a typical path being shown by the 4dotted lines in the figure. Thus, large groups of electrons following similar paths simultaneously, will return together to the vicinity of the grid and prevent other electrons from passing out through the grid G until all of those in the space between the grid G and the anode A have returned to the grid. Then other groups will start out and the operation will be repeated, giving rise to oscillations of a frequency corresponding to the time of travel of the electrons.

The oscillations are assisted or increased by radio frequency fluctuations of potential on the electrodes, caused by the moving charges made up of the electrons, in cooperation with the electrode tuning. There are also optimum relative dimensions for the parts in the tube, but the relations for determining the relative dimensions are quite involved and will not be given here.

The oscillations generated may be utilized in output circuit O to energize the antenna in the manner indicated in the drawing.

I claim:

l. In high frequency apparatus comprising an electron emitting element, an anode, and a grid intermediate said element and said anode, the method of producing high frequency oscillations which comprises propelling a stream of electrons from said electron emitting element towards said anode, deflecting said stream of electrons in a curved path away from said anode and in the general direction of said electron emitting element, and retarding the return flow of said electrons whereby they impinge on said grid with a relatively slow velocity.

2. In a communication system, high frequency apparatus having, in combination, a vacuum tube comprising a substantially cylindrical anode, an electron emitting cathode centrally disposed therein, and a grid surrounding said cathode, a source of potential for supplying a positive potential to said grid and a higher positive potential to said anode, leads extending from said grid and anode to said source, a coil surrounding said anode for producing a magnetic field, a connection between said cathode and the lead extending from said grid to said source, said connection comprising a condenser and an adjustable member arranged to be moved over said lead for tuning purposes.

3. In a communication system, high frequency apparatus having, in combination, a vacuum tube comprising a substantially cylindrical anode, an electron emitting cathode centrally disposed therein, and a grid surrounding said cathode, a source of potential for supplying a positive potential to said grid and a higher positive potential to said anode, leads extending from said grid and anode respectively to said source, a coil surrounding said envelope for producing a magnetic field, a connection between said cathode and the lead extending from said grid to said source, an output circuit coupled to said lead, and modulating means in circuit with the lead extending from said anode to said source.

4. In a communication system, high frequency apparatus having, in combination, a vacuum tube comprising a substantially cylindrical anode, an electron emitting cathode centrally disposed therein, and a grid surrounding said cathode, a source of potential for supplying a positive potential to said grid and a higher positive potential to said anode, leads extending from said grid and anode respectively to said source, a coil surrounding said envelope for producing a magnetic eld, a connection between said cathode and the lead extending from said grid to said source, said connection comprising a condenser and an adjustable member arranged to be moved o-ver said lead for tuning purposes, an output circuit coupled to said lead, and keying means serially connected in the lead extending from said anode to said source. 5. In high frequency apparatus comprising an electron emitting element, an anode, and a grid intermediate said element and said'anode, the v,

method of producing high frequency oscillations which comprises attracting a stream of electrons from said electron emitting element towards said grid, utilizing said anode to attract said stream of electrons from the vicinity of said grid toward said anode, preventing said stream of electrons after having passed said grid from reaching said anode, and retarding the return iiow of said electrons to said grid whereby they impinge on said grid with a relatively low velocity.

6. A high frequency oscillator comprising a vacuum tube having an electron emitting cathode, a. grid substantially surrounding the cathode, an outer electrode outside the grid, means for supplying to the grid a potential which is positive with respect to the cathode and to the outer electrode a still more positive potential, means for producing a magnetic iield in the tube of such direction and strength as at all times to substantially prevent a ow of current to the outer electrode but not prevent passage of electrons from the cathode through the grid into the space between the grid and outer electrode, and circuits extending from said grid and outer electrode to said cathode and tuned to such a high frequency that the mean electron velocity is a major factor in determining the frequency of oscillations.

'7. In a communication system, high frequency apparatus having, in combination, a vacuum tube comprising a substantially cylindrical anode, an electron emitting cathode centrally disposed therein, and a grid surrounding said cathode, a source of potential for supplying a positive potential to said grid and a higher positive potential to said anode, leads extending from said grid and anode to said source, a coil surrounding said anode for producing a magnetic field, individual connections between said cathode and the leads extending from said grid and anode to said source, each of said connections comprising a condenser and an adjustable member arranged to be moved over its respective lead for tuning purposes.

CLARENCE W. HANSELL. 

